This invention relates to a storage apparatus. More particularly, this invention relates to an apparatus with automatic insertion and retrieval of samples from a storage container. More specifically, this invention relates to an apparatus for the preservation of biological specimens at various temperatures, including but not limited to the temperature of liquid nitrogen. This invention also relates to an associated method for storing a multitude of samples, e.g., biological samples.
When properly treated, biological specimens can be stored almost indefinitely at temperatures approaching that of liquid nitrogen so long as that temperature is maintained. However, once the temperature of a specimen is raised, especially to a level where thawing occurs, the integrity of the specimen suffers if the specimen is then refrozen.
Many conventional cryogenic storage units are simple containers with removable racks having multiple shelves. Specimens are inserted and removed from the storage units manually through a door in the top of the unit. Retrieval operations always necessitate the removal of many specimens in the same rack as the desired specimen.
A considerable advance in the mass cryogenic storage of biological specimens was made with U.S. Pat. No. 4,969,336. That patent disclosed the automated moving of specimens along a predetermined path inside a storage tank, with automated insertion and retrieval operations under computerized tracking control.
A further significant improvement in the cryogenic storage arts was introduced with U.S. Pat. No. 5,233,844. That patent discloses a cryogenic storage unit comprising a plurality of independently rotatable storage shelves located one above the other in an insulated chamber. Each shelf supports several pie-slice-shaped trays each carrying a multiplicity of specimens in vials. The shelves each have a pie-slice-shaped opening, with these openings being disposed one above the other to define a vertical access path. To retrieve a particular vial or specimen from the storage unit, the shelf containing the desired specimen is rotated so that the tray containing the specimen is located in the access path. A lift mechanism raises the tray to the top of the unit where a robotic arm retrieves the desired specimen.
The cryogenic storage unit of U.S. Pat. No. 5,233,844, although superior to conventional cryogenic storage units which are manually operated, is subject to the disadvantage of having a significant number of moving parts. Such moving parts suffer from wear and thus require substantial repair and maintenance efforts.
Moreover, automated storage units pursuant to U.S. Pat. No. 5,233,844 suffer from the formation of ice at the access openings to the storage units. This problem is overcome in existing machines by the utilization of heating elements at the access openings. Heating, of course, militates against maintaining desired low temperatures in the storage units.